Cholinesterase (ChE) belongs to specific esterases, which can be divided into two categories, one is acetyl cholinesterase (AChE), also known as true cholinesterase, which can hydrolyze acetylcholine, and play a physiological regulatory role; the other is cholinesterase, also known as pseudocholinesterase (Pseudocholinesterase, PsChE), which can hydrolyze esters of choline but not acetylcholine esters. The other type is cholinesterase, also known as pseudo cholinesterase (PsChE), which can hydrolyze the ester of choline but not acetylcholine ester. Acetylcholinesterase is mainly found in the cytoplasm of neurons and at the joints between nerves and muscles, which is known as the motor end plate; PsChE is mainly found in the plasma, pancreas, and salivary glands, and its physiological function is not clear yet.

Acetylcholinesterase staining solution (copper ferrocyanide) belongs to the Karnovsky and Roots method, and its staining principle is that acetylcholinesterase hydrolyzes iodinated acetylthiocholine, releasing acetic acid and thiocholine, and the sulfur hydroxyl group (-SH) in thiocholine reduces potassium ferrocyanide to potassium ferrocyanide, which binds with copper ions and forms insoluble reddish-brown to dark-brown copper ferrocyanide precipitation at the enzyme-active site and shows up. The active site of the enzyme is shown. The advantages of this staining solution are simple operation, less diffusion of esterase, its disadvantage is the poor permeability of the substrate to the tissue, can be used to observe the central nervous system and peripheral nerve fibers and other changes in disease conditions, but also conducive to the diagnosis of megacolon, enteric neuron developmental anomalies, organic pesticide poisoning can be inhibited by the enzyme, the enzyme activity decreases and the reaction is negative.